An upper bound is 27 queens, which can threaten all squares of a 3D chessboard hyperplane (and the two adjacent ones), which sweeps through the hypercube and smashes the king against a hyperwall. This assumes that the game doesn’t draw after 50 turns.
An upper bound is 27 queens, which can threaten all squares of a 3D chessboard hyperplane (and the two adjacent ones), which sweeps through the hypercube and smashes the king against a hyperwall. This assumes that the game doesn’t draw after 50 turns.
50 moves rule is totally inappropriate in 4D. Let us dismiss that rule here, yes.
An upper bound is 17 queens: 16 threaten all 6^4 inner squares, then the 17th moves to the inner square closest to the king.
Edit: Nevermind, this amounts to the 17th queen checkmating the king on a 3D board with warp sides.